A host reads and writes data to disk arrays with a mirror configuration (RAID1, RAID10: redundant arrays of inexpensive disks) that are connected to a fiber channel (FC) or Ethernet. RAID 1 simultaneously writes exactly the same data to two devices. RAID 10 includes RAID 1 as a constituent element.
In the prior art, RAID1 is given priority in IO access from the host, such as host reading and writing operations. When IO access operations from the host are frequent, it can take a long time to completely rebuild another disk when a disk failure occurs. During this period, the disk array remains in a non-redundant state. Rebuilding refers to the task of rebuilding and copying data from the remaining disk and replacing a failed disk with a new one, which is a hard disk with an RAID configuration.
Japanese patent application publication JP2007094994 discloses a rebuilding method which changes the scale of the rebuilding process whether or not there is IO access from a host. In Japanese patent application publication JP2012014638, the ratio between host IO processing and rebuilding is simply set to achieve a balance between normal IO operations and the rebuilding process.